This invention relates to mass rate of flow meters of the angular momentum type having a swirl generator for imparting swirl to the measured fluid stream and a torque balance reaction generator for removing the imparted swirl. More particularly, this invention relates to such a meter having an improved readout system for indicating the mass rate of flow.
Mass rate of flow meters of the angular momentum type have become conventional for fluid streams, for example, the flow of fuel to an engine. Such flowmeters comprise a casing through which the measured fluid stream flows and in which are disposed a swirl generator and a reaction turbine. The swirl generator imparts an angular velocity to the stream which is removed by a reaction turbine which is restrained against free rotation. The fluid torque exerted in the reaction turbine is proportional to the product of the mass rate of flow of the stream and the angular velocity of the stream.
Jennings in U.S. Pat. No. 2,714,310, issued on Aug. 2, 1955 disclosed the basic system of such a meter utilizing a swirl generator or rotor driven by a constant speed motor, and a turbine restrained by a spiral spring. The angular displacement of the turbine is read out either directly visually, or by a synchro system.
Pustell et al in U.S. Pat. No. 3,538,767 issued on Nov. 10, 1970, and Bauer et al. in U.S. Pat. No. 3,555,900 issued on Jan. 19, 1971, show an improved system wherein the swirl generator includes a plurality of fixed channels, the reaction turbine is restrained by an electromagnetic torque motor, and a speed turbine is driven by the swirling stream. Rotation of the speed turbine generates a pulse train whose pulse repetition rate is a function of angular velocity. Angular displacement of the reaction turbine generates a signal which is a function of the mass flow rate. The two signals are multiplied to energize the torque motor.
Karlby et al. in U.S. Pat. No. 3,164,017 issued on Jan. 5, 1965 shows a Jennings type meter. The swirl generator is motor driven and has a first knife edge magnet fixed in its periphery and a sensing coil disposed in the housing to detect the passage of this magnet. A second knife edge magnet is fixed in its periphery and a second sensing coil is fixed to an arm which is fixed to the reaction turbine to detect the passage of this second magnet. The two pulses so generated each cycle serve to pass clock pulses to a counter to provide an indication of the displacement of the reaction turbine.
Li in U.S. Pat. No. 3,232,110 issued Feb. 1, 1966 shows a mass flow rate meter having a fixed swirl generator; a free running speed turbine and an angular displacement constrained reaction turbine. A permanent magnet is fixed to the speed turbine. A first sensing coil is fixed to the housing to sense the passage of the magnet during each revolution of the speed turbine. A second sensing coil is fixed to the reaction turbine to sense the passage of the magnet during each revolution of the speed turbine. The time between the two sensings is a function of the displacement of the reaction turbine.
The Karlby et al. and Li mechanisms each respectively require a moving sensing coil carried by the reaction rotor with flexible leads carried through the flowing stream and through the water-tight housing, all providing a probable site for early malfunction.